To meet the demand for wireless data traffic having increased since deployment of 4th-generation (4G) communication systems, efforts have been made to develop an improved 5th-generation (5G) or pre-5G communication system. Therefore, the 5G or pre-5G communication system is also called a ‘Beyond 4G Network’ or a ‘Post LTE System’.
The 5G communication system is considered to be implemented in higher frequency (mmWave) bands, e.g., 60 GHz bands, so as to accomplish higher data rates. To decrease propagation loss of the radio waves and increase the transmission distance, the beamforming, massive multiple-input multiple-output (MIMO), full dimensional MIMO (FD-MIMO), array antenna, an analog beam forming, large scale antenna techniques are discussed in 5G communication systems.
In addition, in 5G communication systems, development for system network improvement is under way based on advanced small cells, cloud radio access networks (RANs), ultra-dense networks, device-to-device (D2D) communication, wireless backhaul, moving network, cooperative communication, coordinated multi-points (CoMP), reception-end interference cancellation and the like.
In the 5G system, hybrid FSK and QAM modulation (FQAM) and sliding window superposition coding (SWSC) as an advanced coding modulation (ACM), and filter bank multi carrier (FBMC), non-orthogonal multiple access (NOMA), and sparse code multiple access (SCMA) as an advanced access technology have been developed.
Meanwhile, wireless or mobile (i.e., cellular) communications networks in which a mobile terminal (e.g., user equipment (UE), such as a mobile handset) communicates via a radio link to a network of base stations or other wireless access points connected to a telecommunications network, have undergone rapid development through a number of generations.
The initial deployment of systems using analogue signaling was superseded by second generation (2G) digital systems such as global system for mobile communications (GSM). Second generation systems have themselves been largely replaced or augmented by third generation (3G) digital systems such as the universal mobile telecommunications system (UMTS), which uses a universal terrestrial radio access network (UTRAN) radio access technology and a core network similar to GSM. UMTS is specified in standards produced by the 3rd generation partnership project (3GPP). 3G standards provide for a greater throughput of data than is provided by second generation systems. This trend is continued with the move towards fourth generation (4G) systems which are now widely deployed.
3GPP design specify and standardize technologies for mobile wireless communications networks. Specifically, 3GPP produces a series of technical reports (TR) and technical specifications (TS) that define 3GPP technologies. In particular, 3GPP specify standards for 4G systems including an evolved packet core (EPC) and an enhanced radio access network called “evolved UTRAN (E-UTRAN)”. The E-UTRAN uses long term evolution (LTE) radio technology, which offers potentially greater capacity and additional features compared with previous standards. Despite LTE strictly referring only to the air interface, LTE is commonly used to refer to the entire system including both the EPC and the E-UTRAN. LTE is used in this sense in the remainder of this specification, and also should be understood to include LTE enhancements such as LTE Advanced which offers still higher data rates compared to LTE and is defined by 3GPP standards releases from 3GPP Release 10 up to and including 3GPP Release 12. LTE Advanced is considered to be a 4G mobile communication system by the International Telecommunication Union (ITU).
The trend towards greater data throughput continues with current research efforts developing fifth generation (5G) network technologies. While the form that 5G networks may take and the use cases for such networks are currently unclear, it is probable that 5G networks will include a blend of technologies and will include the capacity to provide extremely high data rates to mobile users in relatively compact geographical areas. This is likely to supplement rather than replace existing wider ranging but lower data rate LTE services.
The focus of the present disclosure is on 5G radio access technologies, for instance in the unlicensed 60 GHz band, which provide for significantly higher peak data rates compared with LTE systems. However, one way in which the 60 GHz spectrum can be exploited is through the deployment of 60 GHz small cells (e.g., through a base station which may be referred to herein as a 5G base station) under the control of LTE macro cells utilizing a core network which may be based upon the EPC. As such, an overview of an LTE network is shown in FIG. 1 and the inter-relationship between LTE macro cells and 60 GHz small cells will be described later in connection with FIG. 2.
FIG. 1 illustrates an overview of an LTE mobile communication network according to the related art.
Referring to FIG. 1, an LTE system comprises three high level components including at least one UE 102, E-UTRAN 104 and EPC 106. The EPC 106 (e.g., core network) communicates with external packet data networks (PDNs) and servers 108. Referring to FIG. 1, interfaces between different parts of the LTE system are shown. The double ended arrow indicates an air interface between the UE 102 and the E-UTRAN 104. For the remaining interfaces, user data is represented by solid lines and signaling is represented by dashed lines.
The E-UTRAN 104 (e.g., radio access network (RAN)) comprises an E-UTRAN node B (eNB), though typically a plurality of eNBs are deployed, which are responsible for handling radio communications between the UE 102 and the EPC 106 across the air interface. LTE is a cellular system in which the eNBs provide coverage over one or more cells.
Key components of the EPC 106 are shown in FIG. 1. It will be appreciated that in an LTE network there may be more than one of each component according to the number of UEs 102, the geographical area of the network and the volume of data to be transported across the network. Data traffic is passed between each eNB and a corresponding serving gateway (S-GW) 110 which routes data between the eNB and a PDN gateway (P-GW) 112. The P-GW 112 is responsible for connecting a UE to one or more external servers or PDNs 108. A mobility management entity (MME) 114 controls the high-level operation of the UE 102 through signaling messages exchanged with the UE 102 through the E-UTRAN 104. The MME 114 exchanges signaling traffic with the S-GW 110 to assist with routing data traffic. The MME 114 also communicates with a home subscriber server (HSS) 116 which stores information about users registered with the network.
An increase in consumer demand for wireless broadband data is evident from the fast uptake of LTE across the world. In view of this, and in view of the high cost associated with increasing the capacity of LTE networks, data service suppliers and operators are increasingly studying how to augment those networks. One such method involves using the unlicensed spectrum to compliment LTE broadband data services. The move to the additional use of unlicensed spectrum is driven in part by the desire to increase data rates to consumers through opening up new parts of the spectrum, but also due to the considerable investment required, and the long regulatory delay incurred, when obtaining new licensed spectrum. Additionally, a substantial portion of the licensed spectrum around existing frequencies used by LTE is already in use. Finding licensed spectrum of sufficient bandwidth to support proposed 5G networks is challenging.
The unlicensed spectrum may be exploited by operators offloading traffic from the licensed spectrum to unlicensed spectrum, for instance in the 2-5 GHz band, thereby making use of, for example, Wi-Fi (via LTE/Wi-Fi interworking), LTE over unlicensed (LTE-U), or license-assisted access (LAA) technology. 3GPP Release 13 is expected to include support for LTE operation in the unlicensed 5 GHz band. The on-going 3GPP study is scheduled to be completed in June 2015 and will also cover the mechanisms for coexistence in the 5 GHz band.
In LAA, a primary LTE cell operating in the licensed spectrum is aggregated with a secondary cell operating in the unlicensed spectrum. That is, LAA may allow for centralized scheduling to be performed by the eNB, which also handles carrier selection for UEs under its control. LTE-U can be considered to provide a broader networking solution to that provided by LAA technology, for example by providing a standalone LTE-U solution where only unlicensed frequencies are used in a network which otherwise operates in accordance with a configuration typical of LTE. While the licensed spectrum is used to provide critical information and ensure quality of service (QoS), the unlicensed spectrum can be leveraged to increase data rate when required.
A result of this use of unlicensed spectrum is that network operators no longer have exclusive access to a spectrum band. Where there is exclusive access to an assigned band, transmissions may be coordinated across the network to allow for the coexistence of multiple base stations and mobile devices through centralized planning of time-frequency resources or through peer-to-peer signaling. In the unlicensed spectrum this coordination is not always possible as there is no requirement for network operators to notify each other of their use of the spectrum.
One option to ensure fair access to the unlicensed spectrum, and to minimize interference, is the use of a listen-before-talk (LBT) procedure to sense carriers before transmission and to facilitate effective sharing of the unlicensed spectrum. The LBT procedure is a contention-based protocol which may be described as a mechanism by which an equipment or component (e.g., a UE or eNB) applies a clear channel assessment (CCA) check prior to using a channel. By using energy detection (as a minimum), the CCA allows the existence of other signals on the channel to be determined. As a result, it can therefore be determined whether or not the channel is clear or occupied.
In LBT, eNB attempts to access a channel only at a pre-assigned time instants are denoted as “transmission opportunities”. At a transmission opportunity, if the eNB has to send data and it is not already transmitting, sensing takes place which is based on the detection of energy in the channel during a predefined time interval. If the detected energy is below a threshold, the channel is deemed to be available and transmission takes place. If the detected energy is above the threshold, the channel is deemed to be busy and no transmission occurs. A coexistence gap provides opportunities to other networks operating in the same band using gaps in LTE transmission. Coexistence gaps are silent gaps, which may be considered to be LTE “OFF” periods. The eNB resumes transmission at the end of each coexistence gap without assessing the availability of the channel. LBT allows for effective data packet transmission between components sharing a network or transmission medium. However, a problem may occur in these networks when a hidden node is present. In this case, a hidden node may be defined as a first node (e.g., a WLAN access point (AP) or an eNB belonging to another network operator) which is visible to a second node (e.g., a UE) but is not visible to a third node (e.g., an eNB), where the third node is communicating with the second node. This lack of visibility may simply be a result of the nodes being out of range of each other, and so the first node is hidden, or invisible, to the third node (and potentially vice versa). A hidden node may also be caused by being around a corner from a directional beam transmission (i.e., the node made be out of the path of the directional beam). The existence of the hidden node may cause problems such as data packet collision and corruption. The existence of hidden nodes may result in interference that cannot be mitigated by the use of the LBT procedure.
As noted above, to meet the continually increasing demand for higher data rates and higher volumes of data transmitted through wireless communication systems, one option is to use a wider frequency band, such as may be available in the extremely high frequency (EHF) band from 30 GHz to 300 GHz, or wider still, for instance to include spectrum around 28 GHz. Radio waves in this band range from 10 mm to 1 mm and so the band is sometimes referred to as the millimeter band or millimeter wave (mmW). In particular, unlicensed spectrum around 60 GHz may be exploited to provide a high data rate service in a small cell, typically supplementing an LTE macro cell. An approximately 8 GHz bandwidth is available in the 60 GHz unlicensed band and this could be used for cellular systems: a concept which may be referred to as pre-5G (pending standardization of 5G technologies). The precise range of the unlicensed 60 GHz spectrum varies between different territories. Referring to Table 1 below, this shows the unlicensed 60 GHz spectrum bands in seven different territories. Table 2 further identifies the maximum equivalent isotropically radiated power (EIRP) in decibel-milliwatts (dBm) for each band together with the maximum transmission power within a beam. For the purposes of the present disclosure the precise unlicensed band under consideration is not relevant, only that directional beams are used.
TABLE 1Upper Limit -EIRP -Max -TerritoryLower limit - GHzGHzdBmdBmAustralia59635213Canada57644327China59644710Europe57665510Japan59665710South Korea57645710USA57644327
Radio waves in the 60 GHz band are subject to high atmospheric attenuation due to absorption by gases in the atmosphere and so are limited in range, though with the benefit of allowing for smaller frequency reuse distances. EHF transmissions are also substantially line of sight and are readily blocked by objects in their path, or reflected or diffracted by building edges.
These limitations on EHF transmissions may be mitigated through the use of beam-forming which can increase effective transmission range. Beam-forming may be classified into transmission beam-forming and reception beam-forming. Transmission beam-forming concentrates a reach region of a radio wave in a specific direction using a plurality of antennas (i.e., an antenna array). Transmission range is increased in the intended direction and is minimized in other directions. Interference to other users in directions other than the intended direction is reduced. In reception beam-forming a reception side concentrates the reception of radio waves from an intended direction using a reception antenna array. The received signal strength from the intended direction is increased and the received signal strength from other directions is minimized.
It will be appreciated that where the unlicensed 60 GHz band is used, then the same need to minimize interference from other users of the spectrum discussed above in connection with LAA also arises. The 60 GHz band is already well used, in particular for point-to-point high bandwidth communication links. It is additionally proposed for use by WirelessHD (also known as UltraGig) for the transmission of high definition video content between consumer electronic devices and by the wireless gigabit alliance (WiGig) which promotes the use of the 60 GHz band for wireless networking in accordance with the Institute of Electrical and Electronic Engineers (IEEE) 802.11ad standard. However, the LBT procedure described above is considered ineffective where highly directional transmissions are used, as is the case for EHF transmissions. In contrast, the transmission scenario envisioned for LAA in the 2-5 GHz band is omnidirectional or sectorial (i.e., the antenna radiation pattern of the transmit antenna has a wide beam width). For example a 5G base station implementing LBT and which has directed its receiver beam in a certain direction may not “hear” the transmission by another nearby 5G base station (or for instance, a WiGig AP). The 5G base station will therefore assume the channel to be free, hence starting a transmission which can cause interference to the victim system (e.g., a 5G base station belonging to a different operator or a WiGig AP). Additionally, LBT is spectrally inefficient, which undermines a significant part of the rationale behind moving to 60 GHz transmissions in the first place.
WiGig attempts to address the problem of interference by using a contention based approach where at any given time the entire channel is allocated to a single user, but users contend for time-slots to be served using a hybrid time division multiple access (TDMA)-carrier sense multiple access (CSMA) scheme based on IEEE 802.11 enhanced distributed channel access (EDCA). WiGig supports up to four transmitter antennas, four receiver antennas, and 128 sectors. Beam-forming is mandatory in 802.11ad, and both transmitter-side and receiver-side beam-forming are supported. The WiGig contention based approach also suffers from spectral inefficiency.
The above information is presented as background information only to assist with an understanding of the present disclosure. No determination has been made, and no assertion is made, as to whether any of the above might be applicable as prior art with regard to the present disclosure.